2016 Vol.36(5)

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2016, 36(5): 0-0.
[Abstract](125) [PDF 879KB](5)
Isothermal Aging Precipitate of TB17 Titanium Alloy
Zhe WANG, Xinnan WANG, Liwei ZHU, Zhishou ZHU
2016, 36(5): 1-6. doi: 10.11868/j.issn.1005-5053.2016.5.001
[Abstract](352) [FullText HTML] (85) [PDF 4654KB](2)
Transmission Electron Microscope (TEM), X-Ray Diffraction(XRD) and Optical Microscope(OM)were employed to investigate the aging precipitation behavior of a new type of ultra-high strength TB17 titanium alloy. The results show that during heat solution treated in the β phase field followed by aging the secondary α phase is nucleated, precipitated and grew on the β phase matrix, and the precipitated phase is lamellar structure which has burgers relation with the matrix. The secondary α phase content is increased rapidly and finally reach a steady-state as aging time increased and the final product of aging consists of α phase and β phase. there is a good linearity relationship between the content of secondary α phase and the hardness of age hardening. The TB17 titanium alloy isothermal phase transformation kinetics can be described by JMAK equation.
Investigation of Dynamic Mechanical Behavior and Damage Characteristics in TC32 Alloy
Mingbing LI, Zhishou ZHU, Xinnan WANG, Yue FEI, Liwei ZHU, Guoqiang SHANG, Jing LI
2016, 36(5): 7-13. doi: 10.11868/j.issn.1005-5053.2016.5.002
[Abstract](302) [FullText HTML] (57) [PDF 10634KB](2)
The dynamic shearing experiment was been done by using split Hopkinson pressure bar(SHPB) technique in TC32 alloy with lamellar, bimodal and basket microstructures. The damage Characteristics of TC32 alloy was investigated by using optical microscope(OP) and scanning electron microscopy(SEM). The results show that the critical fracture velocity is 2400 s-1, 2700 s-1, and 2600 s-1 for lamellar, bimodal, and basket microstructures respectively. The bimodal microstructure exhibit the best Dynamic mechanical behavior compared with the other two microstructures. Adiabatic shear bands(ASBs) and microvoids initiation, growth, and coalescence to damage in adiabatic shear bands(ASBs) were observed in all of three microstructures. Also, microvoids initiation and growth are prior to the interface between ASBs and matrix. Investigation indicated that plastic flow characteristic is not obvious at the interface between ASBs and matrix, which observed long crack in lamellar microstructure. In bimodal microstructure, fibrous a adiabatic shear bands(ASBs) and surrounding region are shown. Because of strong shear deformation, the plastic flow characteristic appears clearly, and primary α phase was elongated. Microvoids initiation is also prior to the α/β phase boundaries. The damage characteristics of basket microstructure are similar to bimodal microstructure. But unlike lamellar and basket microstructures, the microvoids are initiatied when the acicular primary α phase arranged in order is perpendicular to the adiabatic shear bands(ASBs) in lamellar microstructure. ASBs is mostly consisted of equiaxed grains, and the deformation mechanism still wasn't defined.
Effect of Deforming Temperature and Strain on Abnormal Grain Growth of Extruded FGH96 Superalloy
Chaoyuan WANG, Yunpeng DONG, Xiaojun SONG, Shuang Fang, Qiuying YU, Kai LI, Shuyun WANG
2016, 36(5): 14-20. doi: 10.11868/j.issn.1005-5053.2016.5.003
[Abstract](223) [FullText HTML] (48) [PDF 32123KB](5)
Based on the experiments of isothermal forging wedge-shaped samples, Deform-3D numerical simulation software was used to confirm the strain distribution in the wedge-shaped samples. The effect of deforming temperature and strain on abnormal grain growth(AGG) in extruded FGH96 superalloy was examined. It is found that when the forging speed is 0.04 mm/s, the critical AGG occurring temperature is 1100℃, and the critical strain is 2%.AGG does not occur within 1000-1070℃, but still shows the feature of 'critical strain', and the region with strain of 5%-10% has the largest average grain size.AGG can be avoided and the uniform fine grains can be gained when the strain is not less than 15%.
Effect of Pre-sretching Processing on Microstructures and Properties of 2A97 Al-Li Alloy
Juan YU, Zheng LU, Guo'ai LI, Zhaohui FENG
2016, 36(5): 21-25. doi: 10.11868/j.issn.1005-5053.2016.5.004
[Abstract](254) [FullText HTML] (59) [PDF 6881KB](3)
The effect of pre-sretching processing before artificial aging on the microstructures and properties of 2A97 Al-Li alloy was investigated by using tensile test, corrosion test and transmission electron microscope(TEM) observations. The results show that under the same aging process, the tensile strength and the corrosion property of 2A97 Al-Li alloy are greatly increased after 3% pre-sretching; the tensile strength increases 32 MPa, and intergranular corrosion level changes to pitting corrosion. The pre-sretching promotes the T1 phase precipitation and makes its distribution more dispersive and homogeneous at matrix, reducing the content of the δ' phase, while the precipitation of equilibrium phase is restrained during the aging process, consequently improving the tensile strength and the corrosion property.
Predictive Modeling of Mechanical Properties of Welded Joints Based on Dynamic Fuzzy RBF Neural Network
Yongzhi ZHANG, Junhui DONG, Hongling ZHU
2016, 36(5): 26-30. doi: 10.11868/j.issn.1005-5053.2016.5.005
[Abstract](248) [FullText HTML] (57) [PDF 706KB](3)
A dynamic fuzzy RBF neural network model was built to predict the mechanical properties of welded joints, and the purpose of the model was to overcome the shortcomings of static neural networks including structural identification, dynamic sample training and learning algorithm. The structure and parameters of the model are no longer head of default, dynamic adaptive adjustment in the training, suitable for dynamic sample data for learning, learning algorithm introduces hierarchical learning and fuzzy rule pruning strategy, to accelerate the training speed of model and make the model more compact. Simulation of the model was carried out by using three kinds of thickness and different process TC4 titanium alloy TIG welding test data. The results show that the model has higher prediction accuracy, which is suitable for predicting the mechanical properties of welded joints, and has opened up a new way for the on-line control of the welding process.
Influence of Hole Cold Expansion on Microstructure and Fatigue Life of 2124 Aluminum Alloy
Linna YI, Jigang RU, Min HUANG, Deyu SONG, Liang WANG
2016, 36(5): 31-37. doi: 10.11868/j.issn.1005-5053.2016.5.006
[Abstract](345) [FullText HTML] (67) [PDF 14415KB](2)
The change of fatigue life and microstructure of 2124-T851 thick plate after cold expanded with different deformation was studied by fatigue test, TEM, SEM and X-ray diffraction apparatus. The results show that the fatigue life increases with the increase of expanded deformation until the maximum value is reached, and then decreased rapidly with the increase of expanded deformation. At 0.4 mm expanded deformation, fatigue life reach peak value, which is 12.66 times of the non-cold-worked specimens. The microstructure research results show that the residual compressive stress and dislocation cell structure form around the cold-worked holes during the cold expansion, and increase quickly with the expanded deformation. The strengthened layer retarded the fatigue crack growth rate. The appropriate cold expanded deformation can improve the surface roughness of hole, and retard the initiation of fatigue crack, consequently improving the whole fatigue life.
Effects of Thermal Exposure on Structures of DD6 Single Crystal Superalloy with Thermal Barrier Coatings
Jianmin DONG, Jiarong LI, Rende MU, He TIAN
2016, 36(5): 38-43. doi: 10.11868/j.issn.1005-5053.2016.5.007
[Abstract](263) [FullText HTML] (54) [PDF 8042KB](7)
In order to investigate the effect of water grit-blasting and high temperature thermal exposure on the microstructures of DD6 alloy with TBCs, DD6 single crystal superalloy specimens were water grit-blasted with 0.3 MPa pressure, then the specimens were coated with thermal barrier coatings by electron beam physical vapor deposition (EB-PVD). Specimens with TBCs were exposed at 1100℃ for 50 and 100 hours in the air respectively, and then these specimens were subjected to stress-rupture tests under the condition of 1100℃/130 MPa. The results show that grit-blasting doesn't lead into the recrystallization, thermal exposure can induce element interdiffusion between the bond coat and alloy substrate, the residual stress and element diffusion lead into the changes of γ' phase coarsing direction. After stress rupture tests, the secondary reaction zone emerges into a local area.
Laser Rapid Preparation TixAly-TiN Composite Coating
Zhenxi JIN, Chengcheng ZHANG, Guojian DENG, Xiancheng ZHANG, Zhengdong WANG
2016, 36(5): 44-51. doi: 10.11868/j.issn.1005-5053.2016.5.008
[Abstract](247) [FullText HTML] (58) [PDF 23626KB](5)
The TixAly-TiN composite coatings were in-situ synthesized on Ti-6Al-4V alloy surface by using laser nitriding method. The phase composition, microstructure and microhardness were invesitigated. The results show that the coating is mainly composed of TiN reinforced particles and TixAly intermetal matrix. With increase of the depth from the coating surface, the volume fraction of TiN phase decreased and that of TixAly intermetal matrix increased. Moreover, the size of the TiN phase and the microhardness value of the coating decreased with increase of the depth from the coating surface. The microcracks and pores cannot be found in the coating. The thickness of coating is uniform, and forms a good metallurgical combination between coating and substrate. Along the direction of laser melting depth, the elements of N and Al distribute evenly. The microhardness of coating increases significantly, and gradually reduces from coating to the substrate.
Effect of Surface Silicone Coating on Environmental Stress Cracking Resistance of Transparent Polycarbonate Parts
Chenguang YAN, Jian HAN, Junli ZHANG, Yanxiao WANG, Lixiang ZHANG, Chuntai LIU, Changyu SHEN
2016, 36(5): 52-57. doi: 10.11868/j.issn.1005-5053.2016.5.009
[Abstract](298) [FullText HTML] (67) [PDF 12640KB](8)
Environmental stress cracking(ESC) behavior of silicone coated polycarbonate (PC) in ethanol was studied. Stress relaxation of PC and PC/silicone coating under a combined action of ethanol and stress was measured by self-made three point bending equipment. After stress relaxation testing, crack morphology was observed by polarizing microscope. The results indicate that silicone coating is able to improve the stress cracking resistance of PC parts in ethanol. The coated PC shows slower stress relaxation rate and less number of cracks than pristine PC. It is mainly attributed to that the silicone coating can provide barrier effect to the absorption and diffusion of ethanol in PC substrate. Furthermore, the mechanical properties of flexible silicone coating matched fairly well with that of PC, so that the coating is uneasy to peel off from PC substrate during the ESC testing. The silicone coating has a favorable effect to protect PC substrate from ESC under the combined action of solvent and stress.
Effects of Forming Process on Composite mode I Interlaminar Fracture Toughness
Xingyi CHEN, Zengshan LI, Xiao HUANG, Zhejun KOU
2016, 36(5): 58-63. doi: 10.11868/j.issn.1005-5053.2016.5.010
[Abstract](260) [FullText HTML] (58) [PDF 6084KB](2)
In order to compare and analyse the effect of two different kinds of forming process on composite mode I interlaminar fracture toughness, the DCB specimens were tested by using hypothesis inspeetion method.A finite element model was also used to simulate the crack propagation process.The results demonstrate that the average of mode I interlaminar fracture toughness from silicon rubber flexible mold forming is a bit higher than that from metal rigid mold forming.Howevers the variance of mode I interlaminar fracture toughness from the two groups shows no significant difference.The crack propagation process of the two forming process is similar. The established finite element model, which is identical to the test results, can predict the process of the crack expansion effectively.
Fatigue Behaviors of 2024 Aluminum Alloy under Aviation Load Spectrum
Yajun CHEN, Ailun WANG, Fusheng WANG, Xianchao WANG
2016, 36(5): 64-69. doi: 10.11868/j.issn.1005-5053.2016.5.011
[Abstract](276) [FullText HTML] (79) [PDF 3861KB](7)
The fatigue properties of 2024 aluminum alloy under the influence of TWIST on the aviation load spectrum were studied. The aircraft load spectrum was simplified, and the fatigue life of the aircraft was predicted by theoretical analysis, MATLAB program simulation and fatigue was test, and the failure mechanism was observed. The results show that the predicted values of fatigue life are 163800, 158280 and 134249 respectively. Aircraft cruise loads during actual gust load spectrum is simulated, the minimal fluctuation spectrum is ignored. The flight cycles are 92314 and 92321 times respectively. Crack initiation nucleation is originated in the test piece near the surface. Fatigue crack is propagated between intergranular and transcrystalline rupture. Instantaneous, rupture zone and crack propagation can be observed.
Thermal Effect on Bistable Behaviour of T700/3234 Anti-symmetric Cylindrical Shells
Zheng ZHANG, Hao PAN, Gangfei YE, Chen LI, Huaping WU, Guozhong CHAI
2016, 36(5): 70-76. doi: 10.11868/j.issn.1005-5053.2016.5.012
[Abstract](242) [FullText HTML] (59) [PDF 3066KB](3)
The temperature effects on the bi-stable characteristics of T700/3234 anti-symmetric carbon-fiber composite structure were studied. Three different layup specimens were prepared through composite molding process.The two points loading method was used in the experiment. The modified experimental testing machine (the experimental testing machine could be used to induce the bistable composite shell to snap between the two stable shapes, and continually capture the data in the experimental process.) was related to tensile testing machine at present. The load-displacement curvatures under the temperature of 20℃, 40℃, 60℃ and 80℃ were given. The snap load was recorded and the photos were taken in the experimental process. After the experiment, the detailed data of curvature and twisting curvature were obtained by image processing technology. The variation law of the coiled-up radius, out-of-plane displacement, maximum snap-through and snap-back loads were analyzed. The effect on the composite structure was also discussed.The result shows that the thermal effect is vital to the bistable snaps process, and corresponding influence trends to the snap through and snap back process are given.
Tensile Strain Hardening Behavior and Fractography of Superalloy GH39
Hui WANG, Minghe CHENG, Chengxiang ZHANG, Haiyan ZHAO, Pengfei WANG, Xiaojing LEI
2016, 36(5): 77-81. doi: 10.11868/j.issn.1005-5053.2016.5.013
[Abstract](254) [FullText HTML] (53) [PDF 5363KB](4)
The strain hardening behaviour and fractography of superalloy GH39 was investigated by tensile test at different strain rates. Results indicate that strain hardening behaviours are different during the deformation process. True stress-strain curve obeys the Hollomon relationship partly. The strain hardening exponentn in this stage is constant in the initial plastic stage. However, the value of n increased with true strain ε increasing when true strain is between 0.014 and 0.13. A lot of deformation twinning can be found, the twins and dislocations worked together to increase the value of n. The strain hardening exponent is increased lightly with the strain rate increasing, SEM observations show that in the case of low strain rate, the fracture mode is typical ductile, but there is a tendency from ductile to brittle fracture with increasing the strain rate.
Research and Progress of Thermomechanical Treatment of Al-Li Alloys
Xiuliang WU, Ming LIU, Guoai LI, Jigang RU, Junzhou CHENG, Zheng LU
2016, 36(5): 82-89. doi: 10.11868/j.issn.1005-5053.2016.5.014
[Abstract](319) [FullText HTML] (75) [PDF 682KB](6)
The strengthening and toughening mechanism of aluminum lithium alloy treated by thermo-mechanical processing have been summarized, and the effect on the evolution of microstructures, grain structure and precipitation, were discussed and analysed deeply. The precipitation sequence and behavior of the main precipitation phase were modified by the thermo-mechanical processing, stimulating the forming of fine dispersion combined particles of δ', θ"/θ', T1, and S"/S' phases, uniformly distributed in the matrix, which significantly improved the relationships of strength and the plastic toughness, with the inhibiting of broadening of precipitate free zones, and of the precipitation and coarsening of strengthening particles at the grain boundary.The density of solute atom and vacancies significantly raised up after solution treating, and retained as supersaturated solid solution after water quenching, which acted as the driving force for the precipitation during subsequent aging. Pre-deformation and pre-aging significantly increased the density of fine dispersion strengthening particles of δ' and G.P. zones, which uniformly nucleated in the matrix, and the combined strengthening phases of δ', θ"/θ', and T1 were obtained after high temperature second aging, controlling the size and volume fraction of these particles.Refined grain and optimal grain structure were achieved by new and typical thermo-mechanical processing, and the proportion, size, and oriented relationship of main strengthening particles of δ', θ"/θ', and T1 phases were optimized.At last, the research direction of new thermo-mechanical treatment on the large scale rolled plates and hot worked forgings is pointed out, such as age forming, to meet the need of light high performance of new aluminum lithium alloys used for the large aircrafs and heavy lift launch vehicles.
Progress on Research of Contact Resistance of Carbon Nanotubes
Lifeng DAI, Libao AN, Jia CHEN
2016, 36(5): 90-96. doi: 10.11868/j.issn.1005-5053.2016.5.015
[Abstract](245) [FullText HTML] (69) [PDF 669KB](6)
The high contact resistance of carbon nanotubes (CNTs) with metal is one key factor that retards the application of CNTs in micro-and nano-electronics devices. This paper reviews recent research progress on the contact resistance of CNTs from two aspects, they are the formation and improvement of the CNT's contact resistance. Theoretical studies of the contact resistance of CNTs using the first principles and experimental investigations into the effect of metal work function on the interface barrier were introduced. Results show that the contact resistance is low when there is a weak hybrid effect and large contact length between the metal and CNTs, and the closer the work function of the metal to that of the CNTs, the lower the barrier height. The commonly used methods for improving the contact resistance of CNTs, including ultrasonic nanowelding, high temperature annealing, metal deposition, and local Joule heating were presented, and the improvement of device performance using these methods was analysed. Among these methods, local Joule heating is more ideal at present time since it is with the advantages of simple operation, high degree of automation, less device damage, and low cost.

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